Proper fuel pressure on heavily modded 1g, 2g timing, pump gas, 10.0 afr, no knock...

[jamesfoster]

So this is the deal, I have a 90 gsx with a 2.3 stroker, Aeromotive AFPR, 60-1 turbo, 8.8:1 pistons, 3" maf and maf translator, 850cc inj, walbro 255, dsmlink etc etc.. This is the problem.

Today we put the 2g timing map in the car, and adjusted the fuel sliders to what the dsmlink manual says should be about an 11.5-12.0 afr, but my friend who was helping me tune everything says we need to have the fuel pressure set at 43.5 which is obviously the 2g fuel pressure. The car reads 10.0 afr as soon as I put my foot down. although im boosting 20psi and getting no knock we cant seem to lean it out. (also I'm pretty sure my stock o2 sensor needs to be replaced, it seems to be reading incorrect voltage. I'm doing that tomorrow.)

So should I be running 2g fuel pressure or bring it back to 1g fuel pressure and try and lean it out? No matter what I do I can't seem to lean the damn thing out at all. We pulled out enough fuel for it to be running 13.0 afr's and it still read 10.0. So what I think is my afr gauge (AUTOMETER NEXUS) is not reading correctly, and I also think my factory o2 sensor is not working correctly. What else could it be?

-James

 

[silver bullit]

Time to test the o2 and the gauge

 

[Mr Peepers]

You need a wideband o2 setup to actually know what afr you are running.

Narrowband is to afr what the stock boost gauge is to boost.

Your stock o2 sensor(narrowband) is only accurate around stoich, 14.7:1, and will only tell you if you are richer or leaner than that. Your AF gauge only reads the voltage from your narrowband o2 sensor.
For WOT tuning, a WBo2 is needed to tell your true afr.

BTW, upping the fuel pressure to 43.5psi will make it run richer than DSMlink will estimate, it still thinks you are running 1g base fuel pressure, 37 psi. No reason to run 2g fuel pressure just because you are on a 2g timing map. You can however compensate for it by increasing deadtime and taking out more global %, but if you have plenty of injector I see no need to.

 

[jamesfoster]

You need a wideband o2 setup to actually know what afr you are running.

Narrowband is to afr what the stock boost gauge is to boost.

Your stock o2 sensor(narrowband) is only accurate around stoich, 14.7:1, and will only tell you if you are richer or leaner than that. Your AF gauge only reads the voltage from your narrowband o2 sensor.
For WOT tuning, a WBo2 is needed to tell your true afr.

I have an autometer nexus wideband. I think it's not working properly. How would I test it?

 

[Mr Peepers]

Sorry I thought I saw a narrowband when I googled it.

Be sure that your GM maf is calibrated, calculated AF ratio on DSMlink is for 850 injectors under props, no boost leaks, and set your fuel pressure back to 1g turbo specs.

 

[jamesfoster]

Sorry I thought I saw a narrowband when I googled it.

Be sure that your GM maf is calibrated, calculated AF ratio on DSMlink is for 850 injectors under props, no boost leaks, and set your fuel pressure back to 1g turbo specs.

Yeah we made sure the maf translator was calibrated today before we started tuning. Everything is set right, I'll check for boost leaks tomorrow but I'm pretty sure everything is clamped down tight. And the damn thing is still reading 10.0 but I'll go over everything again tomorrow and update the thead.

-James

 

[JayRolla]

How much fuel have you pulled to see if it will lean out? I would also go back to 37psi fp but I dont think that will help your issue.

 

[jamesfoster]

How much fuel have you pulled to see if it will lean out? I would also go back to 37psi fp but I dont think that will help your issue.

We pulled out 18% from 2500-4000 rpms, 22% from 4500-6000, and 23% from 6500-8000. And the car STILL was reading 10.0 on the wideband. But the front o2 was reading .76 volts. However even with taking out 1%, 5% and 6% the front o2 still read right around .76 volts.

So basically no matter what we did, the wideband kept reading 10.0 and the front o2 kept reading around .76 volts. (which would indicate the car running dangerously lean.)

What the hell is going on?

 

[BeatupVR4]

So this is the deal, I have a 90 gsx with a 2.3 stroker, Aeromotive AFPR, 60-1 turbo, 8.8:1 pistons, 3" maf and maf translator, 850cc inj, walbro 255, dsmlink etc etc.. This is the problem.

Today we put the 2g timing map in the car, and adjusted the fuel sliders to what the dsmlink manual says should be about an 11.5-12.0 afr, but my friend who was helping me tune everything says we need to have the fuel pressure set at 43.5 which is obviously the 2g fuel pressure. The car reads 10.0 afr as soon as I put my foot down. although im boosting 20psi and getting no knock we cant seem to lean it out. (also I'm pretty sure my stock o2 sensor needs to be replaced, it seems to be reading incorrect voltage. I'm doing that tomorrow.)

So should I be running 2g fuel pressure or bring it back to 1g fuel pressure and try and lean it out? No matter what I do I can't seem to lean the damn thing out at all. We pulled out enough fuel for it to be running 13.0 afr's and it still read 10.0. So what I think is my afr gauge (AUTOMETER NEXUS) is not reading correctly, and I also think my factory o2 sensor is not working correctly. What else could it be?

-James

Raising/lowering your fuel pressure will only make your injectors act larger/smaller, respectivly. It's just an old trick from 80's and early 90's EFI cars because they didn't have the ability to get into the computer and change settings like we do today.

If your computer controls on times thinking it has 38psi base fuel pressure then at 43psi more fuel will be injected in, making 450cc injectors acting like say 480's (Just throwing these numbers out there)

The only reason for an adjustable regulator on a DSM with the Link is to overcome FPR overrun and keep your trims in line. Set the fuel pressure to what the computer thinks it is and simplify your tuning, otherwise it's just another "variable" to have to worry about.

Even though I have heard that to a point higher fuel pressure is preferred as it helps with atomization when the injector is actually open, so my vote would be to stick with the 43.5psi (or 3bar/atmospheres) base, which is the industry standard BTW. Otherwise your shortchanging yourself with your injectors (I.E. they flow LESS than what you paid for )

 

[gsx rated98]

why dont you put your logs up on DSMLink forums, you will probably get a much better resopnce with the posted logs.

 

[jamesfoster]

Raising/lowering your fuel pressure will only make your injectors act larger/smaller, respectivly. It's just an old trick from 80's and early 90's EFI cars because they didn't have the ability to get into the computer and change settings like we do today.

If your computer controls on times thinking it has 38psi base fuel pressure then at 43psi more fuel will be injected in, making 450cc injectors acting like say 480's (Just throwing these numbers out there)

The only reason for an adjustable regulator on a DSM with the Link is to overcome FPR overrun and keep your trims in line. Set the fuel pressure to what the computer thinks it is and simplify your tuning, otherwise it's just another "variable" to have to worry about.

Even though I have heard that to a point higher fuel pressure is preferred as it helps with atomization when the injector is actually open, so my vote would be to stick with the 43.5psi (or 3bar/atmospheres) base, which is the industry standard BTW. Otherwise your shortchanging yourself with your injectors (I.E. they flow LESS than what you paid for )

Ok that is exactly the response I wanted to hear on the fuel pressure subject, and that's exactly what Bob was telling me.

 

[BeatupVR4]

Well give Bob a high-five next time you see him.

 

[jamesfoster]

why dont you put your logs up on DSMLink forums, you will probably get a much better resopnce with the posted logs.

I'm going to, I just wanted to ask here first.

 

[Mr Peepers]

Raising/lowering your fuel pressure will only make your injectors act larger/smaller, respectivly. It's just an old trick from 80's and early 90's EFI cars because they didn't have the ability to get into the computer and change settings like we do today.

If your computer controls on times thinking it has 38psi base fuel pressure then at 43psi more fuel will be injected in, making 450cc injectors acting like say 480's (Just throwing these numbers out there)

The only reason for an adjustable regulator on a DSM with the Link is to overcome FPR overrun and keep your trims in line. Set the fuel pressure to what the computer thinks it is and simplify your tuning, otherwise it's just another "variable" to have to worry about.

Even though I have heard that to a point higher fuel pressure is preferred as it helps with atomization when the injector is actually open, so my vote would be to stick with the 43.5psi (or 3bar/atmospheres) base, which is the industry standard BTW. Otherwise your shortchanging yourself with your injectors (I.E. they flow LESS than what you paid for )

You are completely right and make a great point.
DSMlink most likely doesn't factor in the 1g basefuel pressure when calculating fuel, only the cc you input for a:f. And since the 850's are rated [email protected], it would be fitting to have the fuel pressure at 43.5 for simplicities sake.